Micropollutants removal from aquaculture water using layer-by-layer self-assembled nanofiltration membranes

Abstract

Micropollutants (MPs) in aquaculture water are directly related to human health, but largely overlooked. The conventional water treatment technologies could not effectively remove MPs, and new technologies have been pursued with high MP removal rate, low cost and small footprint. This paper reported the first endeavor of using layer-by-layer (LBL) hollow fiber (HF) nanofiltration (NF) membranes to treat real aquaculture water. We compared three types of membranes with various surface chemical properties and pore sizes assembled by different polyelectrolytes (PEs). The MPs removal rates and operation stability of three NF membranes were studied in flocculation (Floc.)/ultrafiltration (UF)/NF, Floc./NF and direct NF processes. The best poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH) NF membrane showed almost 100 % MPs removal in Floc./UF/NF, and above 95 % in direct NF process. Stable permeance was observed in three 24 h cycles for three processes. The correlation hot spot analysis between the physical properties and removal rates of MPs confirmed importance of size exclusion as the important factor for removal of MPs. The organic humus, rather than inorganic silicon and calcium, was found as the main foulant, which increased slightly the pore size of the LBL membranes with small pores, but blocked pores of membranes with large pores, affected the rejection for ions as well. The cost assessment based on (PSS/PAH)_2.5 showed a total cost below 0.75 ¥/ton water, which is feasible to efficiently remove MPs from aquaculture water by NF membrane process.